Such an oil separator is known for example from EP 1 559 876 A2. This known oil separator comprises a plurality of cyclones for separating the oil from the blowby gas, wherein each cyclone comprises a bowl, which is formed integrally with a bottom shell of a cylinder head cover, and an immersion tube, which is formed integrally with a top shell of the cylinder head cover. The cyclones in this case therefore form an integral component of a twin-shelled basic body of the cylinder head cover and are manufactured together with the basic body.